(1) Field of the Invention
This invention relates to cross-linked lignin gels and processes for making same. More particularly, this invention relates to improved lignin-based carrier useful for the sustained release of pesticides.
The effectiveness of pesticides is controlled by the amounts of toxicity, chemical degradation, biological degradation, run-off, leaching and evaporation.
The reduction of losses of pesticides can be accomplished in developing pesticides insensitive to the chemical, physical and biological means of reducing their effectiveness. Another is the development of delivery systems which protect the pesticide from degradation and limit its availability to leaching, run-off and volatilization, while releasing the pesticide at a rate sufficient for effective biological control. In this later method the pesticide is placed in a matrix which has both the chemical and physical properties necessary to inhibit the undesirable pathways of agent removal. Controlled release thus extends control to both the length and the degree of availability of biologically active material. This is in contrast to the older, slow release systems, which are systems containing several times the normal single dose of active ingredient and which provide for replacement of agents at a rate giving meritable increases in the length of time of activity.
(2) The Prior Art
One method of controlling the release of pesticides using a lignin polymer is provided in U.S. Pat. No. 3,813,236 to G. G. Allan. The Allan patent discloses chemical co-valent bonding of a pesticide to a lignin polymeric substrate. The pesticide is released by destruction of co-valent chemical bonds.
Another example of using lignin for controlling the release of pesticides is disclosed in U.S. Pat. No. 3,929,453 to Dimitri and Falkehag. Dimitri and Falkehag disclose physical bonding of a lignin polymer and pesticide.
Although it is known to form controlled release systems based on alkali lignins, it is the purpose of this invention to provide an improved lignin matrix for this purpose in which a gel is formed by cross-linking the lignin molecules with formaldehyde glyoxal, glutaric dialdehyde or combinations of epichlorohydrin and the difunctional aldehydes in such a manner as to form a reswellable gel. For the purpose of this invention, a lignin gel shall mean a three-dimensional physically or chemically cross-linked matrix which can be repeatedly dehydrated and reswollen to its original volume.
The cross-linked lignin gels of this invention are used to produce sustained release compositions by physically mixing organic pesticides with an improved carrier comprising a cross-linked, reswellable lignin gel. It is, therefore, the general object of this invention to provide cross-linked lignin gel for use in a sustained release composition having a pesticide interspersed and physically bound throughout the cross-linked, reswellable alkali lignin gel.
Another object of this invention is to provide processes for producing the cross-linked gel and for interspersing a pesticide throughout the gel by physical contact forming a composite.
It is a specific object of this invention to provide a controlled release pesticide system comprising as a composite, a pesticide interspersed throughout an alkali lignin-formaldehyde cross-linked matrix whereby the release rate of the pesticide is accomplished through the diffusion of the pesticide through the alkali lignin matrix or through degradation or dissolution of the lignin matrix or a combination of both.
Other objects, features and advantages of this invention will become evident from the foregoing detailed description.